Advanced technological uses for wire and cable have imposed many new requirements upon traditional wire and cable specifications and functions. In missile and aerospace environments, for example, the need for lighter weight cabling is directly related to aircraft performance and operating cost. Also, wiring is often required to meet stringent tensile strength specifications, since it is contemplated that the missile or aircraft will have to fly at ever increasing speeds.
The aforementioned U.S. Pat. No. 5,103,067, teaches the use of silver coated aramid fibers fabricated into a mesh layer for shielded wire and cable.
In order to achieve cable of high conductivity, light weight, high tensile strength and flexibility, it is contemplated to use silver coated aramid fibers to replace the traditional conductive metal strands of the central conductive wire core.
Silver-coated aramid fibers for center conductor core applications, however, do not presently have enough conductivity to meet the specifications for high technological use. To increase the conductivity of the metal-coated aramid fibers, it is necessary to increase the thickness of the silver coating. However, the present plating limit for the silver thickness is generally thirty weight percent (30 wt %), produced by traditional plating methods.
The invention has fabricated silver-coated aramid fibers of higher conductivity by means of coating additional silver upon the aramid fibers via an electrochemical process. It is, therefore, now possible to provide silver-coated aramid fibers as a replacement for traditional wire and metal conductive core elements.
Cable fabricated with these improved fibers have a clear weight advantage, as well as having improved flexibility and tensile strength, over traditional cable featuring a metallic wire core.
The electrochemical process of this invention, allows for precise control of metal thickness, thus producing layers of silver to meet demanding and stringent conductivity requirements.
Electrochemical deposition by itself cannot provide acceptable coatings due to its poor adherence to the fiber core. Plating by itself is limited in the amount of metal that can be coated upon the fiber base.
The invention has discovered, however, that first plating the silver in any thickness up to its limits, and then applying an additional thickness of silver by electrochemical plating is possible, and highly favorable.
The success of the inventive method, and new cable article resulting from the new fabrication technique, is due to the improved adherence of the silver electrochemically deposited upon an already plated silver base layer.
The combination of the two coating methods provides a silver layer whose thickness is much greater than that previously achieved, i.e. substantially beyond the previous limit of thirty weight percent (30 wt %.). The added metal thickness is generally several hundred weight percent of the fiber. Therefore, the core conductivities equal that of pure metal wired cores alone. The conductive fibers of this invention are approximately five hundred times more conductive than the chemically plated fibers of the prior art.
The cable fabricated with a silver-coated, aramid fiber as the central core will be more flexible and of greater tensile strength. The new metal-coated fiber core eliminates the previous cracking problem inherent with cables containing metal wire cores flexed, bent or stretched beyond their physical limits.
The main advantage of the invention, however, is the substantial reduction in weight of the cable of the invention compared with standard cable having a metal wire core.